The present invention relates generally to controllers for a combustion system for a gas turbine. In particular, the invention relates to a combustor control algorithm for fuel splits and nitrogen oxide/nitrogen dioxide (NOx) leveling.
Industrial and power generation gas turbines have control systems (“controllers”) that monitor and control their operation. These controllers govern the combustion system of the gas turbine. Dry Low NOx (DLN) combustion systems are designed to minimize emissions of NOx from gas turbines. The controller executes an algorithm to ensure safe and efficient operation of the DLN combustion system. Conventional DLN algorithms receive as inputs measurements of the actual exhaust temperature of the turbine and the actual operating compressor pressure ratio. DLN combustion systems typically rely on the measured turbine exhaust temperature and compressor pressure ratio to set the gas turbine operating condition, e.g., desired turbine exhaust temperature, total combustor fuel flow, fuel split schedules, and inlet bleed heat flow.
Conventional scheduling algorithms for DLN combustion systems do not generally take into account variations in compressor inlet pressure loss, turbine back pressure, or compressor inlet humidity. Conventional scheduling algorithms generally assume that ambient conditions, e.g., compressor inlet humidity, compressor inlet pressure loss, and turbine back pressure remain at certain defined constant conditions or that variations in these conditions do not significantly affect the target combustor firing temperature.
Compressor inlet pressure loss and turbine back-pressure levels will vary from those used to define the DLN combustion settings. The NOx emissions from the gas turbine may increase beyond prescribed limits, if the conventional DLN combustion system is not adjusted as environmental conditions change. Seasonal variations in humidity or changes in turbine inlet humidity from various inlet conditioning devices, e.g., evaporative cooler, fogging systems, can influence the operation of a DLN combustion system. As the ambient conditions change with the seasons, the settings of DLN combustion systems are often manually adjusted to account for ambient seasonal variations.